The regular way of requesting a payment every second or so is not suited to the mobile network, where opening a connection may take a while, and sending only a single request over that connection is wasteful.
Thus, at the request of Samsung Internet, Coil created a batched payment version of the extension. For now this is a special version of the extension, but it may be folded into the main branch.
Batched payments were implemented in the extension by [??? didn't get name ... DJ ???] but were never released. The current extension does not support batched payments.
If we go the route of allowing web developers to set their own timing (as proposed here there's another caveat: batched payments.
These batch requests could throw off the timings of the example script considerably, and might result in stroboscopic content that switches off and on. I am currently uncertain how to proceed here.
Maybe a new property batched as a flag to warn people batched payments are being made? Then we'd have to define exactly what a batched payment is etc.
It's definitely NOT only paying on unload
Essentially it pays 5 seconds worth immediately, then a little bit more after 10 seconds, in gradually increasing intervals over the first minute. It then switches to PostPay mode, where it pays AFTER usage, again in increasing intervals.
There's a description of the schedule in the first draft of the PR here.
IIRC it's changed since then though (with no updated description)